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Hess’s Law Lab Argumentative

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  • Pages: 5
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  • Category: Energy Law

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Finding the Molar Enthalpy Change of sodium bicarbonate by using Hess Law

Research Question

By using Hess’ Law, can the Molar Enthalpy Change of sodium bicarbonate be calculated?


If we are attempting to determine the enthalpy change of the thermal decomposition of Sodium Bicarbonate, then Hess’s Law will be will be the most effective.


Sodium bicarbonate, more commonly known as baking soda, has many uses in todays world, its main purposes are for cleaning, baking, and medicine. Some of the most common uses for sodium bicarbonate, or baking soda, are relieving ulcer pain, removing splinters, sunburn remedy, deodorant, enhanced sports performance, insect bites, teeth whitener, foot soak, exfoliation, detox bath, and an antacid (Mercola)

In baking, sodium bicarbonate or baking soda is combined with moisture and an acid (like yogurt, chocolate, buttermilk, honey, etc.) and this results in a chemical reaction that produces carbon dioxide, or CO2 , bubbles that start to expand under higher temperatures, like inside an oven, causing baked goods to rise. This process is an almost instant reaction when the ingredients are mixed together. If a Baking recipe calls for baking soda, it needs to be baked immediately, or else they will fall flat!


Hess’ Law states that the heat released or absorbed in a chemical process is the same whether the process takes place in one or in several steps. This law is also known as the law of constant heat summation. Molar Enthalpy is the transfer of heat in a reaction of one mol. Heat capacity is an important property and it is used in heat transfer and other calculations. The equations used in this experiment to determine molar enthalpy change are 1) Molar enthalpy = ΔH/n, ΔH is the change in thermodynamic potential divided by the number of moles; Molar enthalpy is expressed in KJmol. 2) ΔH = -Q, The change in thermodynamic potential, ΔH, is the negative amount of heat transferred, Q; ΔH is expressed in KJ. 3) Q = mcΔT. Where Q is the amount of heat transferred, m is the Mass (g), c is the Specific Heat Capacity of a material (Jg ℃), and ΔT is the change in temperature(℃); Q is expressed in J (EMSB).


1. Make sure to have safety garments and gear on, goggles and aprons, before starting the experiment 2. Calculate how much of a 3M HCl solution and water need to be mixed to dilute the acid to a 2M HCl solution 3. Pour 50 ml of the 2M acid into a styrofoam cup

4. Record the temperature of the HCl
5. Place a mass boat on an electronic scale and zero the scale, measure out 8.4 g of solid NaHCO3 6. While recording the temperature of the acid every 30 seconds, slowly pour the NaHCO3 into the acid in the styrofoam cup, avoid overflows or spillage of substances 7. Record the temperature until a maximum or minimum is reached, either 4 consecutive measurements or until the temperature starts to drop (maximum) or rise (minimum) 8. Repeat steps 1-7 four more times to have a total of 5 trials, after every trial completely rinse out the styrofoam cup and the thermometer to remove any left over substances that could affect the experiment and create invalid results causing the experimenter to redo the trial 9

Conclusion and Evaluation

The results were calculated to give an average specific heat of .25± .12Jg℃ for copper, while the actual is .39Jg℃. The experiment gave a calculated average that has a percent error of 35.897%. The only trial with a specific heat close to copper is trial 1 which was only off by .03Jg℃, all other trials were off by .1 to .2Jg℃ off. The data collected during experimentation resulted with trial 2, 3, and 4 being relatively similar in specific heat and trial 1 and 5 to be higher outliers that were actually more accurate than the 3 precise trials. With a percent error so high the experiment had many flaws that affected the results, though those flaws seemed to be less prevalent in trial 1, which had the most accurate result. Weaknesses

The usage of a different scale during trials 4 and 5
Use of analog measuring devices resulted in high uncertainties Experimenting on 2 different days, change of classroom environment Misreading the temperature of the thermometer during the experiment


Experiment in 1 day rather than 2
Use the same scale every time
The use of digital tools and not analog, analog creates higher uncertainty Cool off all tools, try to recreate the conditions as close as possible to trial 1; cooled cup, and cooled thermometer


consistent mass of metal through whole experiment
the use of some digital equipment

The experiments weaknesses were greater than the strengths, thus leading to a higher percent error. If the experiment were to be redone there are steps that can be taken to make the experiment even more accurate. If the experiment is done with vernier probes instead of alcohol thermometers, the uncertainty would have been greatly reduced. The thermometer had an uncertainty of 1℃ and the temperature changed between 1.7 to 3.2 ℃, this creates an uncertainty of 59% to 31% just for one of the uncertainties. If a vanier probe was used the uncertainty would have been between 12% and 6%, which is about 5 times less. Also the calorimeter was an open system meaning the system was in contact with the surroundings, if a lid is put on top then the calorimeter would be more accurate because it is now a closed system.

The hypothesis is correct, an experimenter can find the specific heat using calorimetry, but not with perfect accuracy. If a few adjustments are made then the experiment could be more accurate.

The knowledge of copper’s specific heat is greatly valued for many reasons, copper is a very commonly used metal, it is in cars, planes, computers, phones, etc. Many cars have copper wiring and have copper in their radiators, and recently with the rising production of electric cars more and more copper is being used in engines as wiring for electrical current. Copper is also used for electric currents is computers, with the knowledge of specific heat, a manufacturer can know how powerful a cooling agent needs to be to make sure the copper wiring does not overheat. Specific heat has allowed for the varied usage of copper and other metals in daily lives, specific heat helps create materials and machines that work more effectively and efficiently.


“Calorimeters and Calorimetry.” The Physics Classroom. The Physics Classroom,, n.d. Web. 08 Oct. 2014.

“Definition of Calorimetry.” Chegg. Chegg Inc, n.d. Web. 10 Oct. 2014.

Leon, Nelson De. “Specific Heat.” IUN. N.p., n.d. Web. 07 Oct. 2014.

Mycheme. “MyChemE.” MyChemE. WordPress, 31 Aug. 2013. Web. 08 Oct. 2014.

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